热处理对Zn-6%Al-3%Mg镀层微观组织与耐蚀性的影响

Effect of Heat Treatment Process on Microstructure and Corrosion Resistance of Zn-6%Al-3%Mg Coating

采用两种工艺(500℃-10 min,700℃-10 min)对Zn-6%Al-3%Mg镀层钢板进行加热处理,通过扫描电镜(SEM)、X射线衍射(XRD)和中性盐雾实验对原始样品和两种热处理样品的耐蚀性、腐蚀形貌和物相进行观察分析,对比研究了锌铝镁镀层在高温加热条件下镀层组织结构及耐蚀性的变化规律。结果表明,Zn-6%Al-3%Mg镀层钢板经过500℃-10 min热处理后,镀层形貌、物相及腐蚀产物种类与原始样品类似,腐蚀失重和增重也与原始样品基本相同,可以认为该热处理工艺对其微观组织和耐蚀性的影响不大。经过700℃-10 min热处理后,镀层组织从单层多相结构转变为分层多相结构,腐蚀产物中有较多Fe的氧化物,主要由析出到镀层表面的富铁相形成,富锌镀层仍然完整覆盖在钢基体表面,腐蚀增重达到原始样品的3.2倍,腐蚀失重达到原始样品的2.2倍。

The Zn-6%Al-3%Mg coated steel plates were subjected to post-heat treatments at 500℃-10 min and 700℃-10 min,respectively.Then the microstructure,phase composition and corrosion resis-tance of the Zn-6%Al-3%Mg coated steel plates before and after heat treatment were comparatively char-acterized by SEM,XRD and neutral salt spray test.The results show that the morphology,phase compo-sition and corrosion products of Zn-6%Al-3%Mg coated steel plate after heat treatment at 500℃-10 min are similar to those without heat treated ones,their corrosion mass changes are basically the same.How-ever after heat treatment at 700℃-10 min,the coating structure changes from single-layer of multiphase structure to multi-layer of multiphase structure,it is worth noting that there are more Fe oxides in the cor-rosion products,which are mainly formed by the iron-rich phase precipitated on the surface of the coat-ing.After corrosion test,the zinc-rich surface coating on the steel substrate kept completely intact,while the corresponding corrosion mass gain is 3.2 times of the un-heat treated ones,on the other hand,the corrosion mass loss is 2.2 times of the un-heat treated ones.